1. Field of the Invention
The present invention relates to a liquid supply method and apparatus that are used in the preparation of solutions. Specifically, the present invention relates to a liquid supply method and apparatus that are used to supply a solution which is to be supplied such as an electrolytic aqueous solution to a primary fluid such as ultrapure water, and to prepare a solution that can be used as washing water for electronic material.
2. Description of Related Art
In the manufacture of electronic material such as semiconductor devices and liquid crystal panels, when a substrate is washed using ultrapure water or when a wafer is cut by a dicing machine, because the ultrapure water has a high specific resistance static electricity is generated and there are occurrences of electric breakdown or the absorption of minute particles. This has marked adverse effects on the substrate yield.
Therefore, in order to solve this problem, a method is known in which the specific resistance of the ultrapure water is lowered by dissolving an electrolyte such as, for example, carbon dioxide or ammonia in the ultrapure water.
In the processes of washing and dicing a silicon wafer, the specific resistance tends to vary frequently because there is considerable variation in the flow rate of the ultrapure water.
One method of suppressing variation in the specific resistance is the technology disclosed in U.S. Pat. No. 6,518,721. In the method described here, the ultrapure water is divided into two branch flows that each have a different flow rate. An electrolyte is then dissolved into the branch flow having the smaller flow rate, and the electrolytic aqueous solution thereby obtained is then merged with the branch flow having the larger flow rate.
As a result, variations in the specific resistance can be suppressed even if variations occur in the flow rate of the original ultrapure water.
However, in this method, because the mixing rate of the electrolytic aqueous solution with the ultrapure water is slow, if there is a considerable variation in the flow rate of the original ultrapure water, then it is difficult to maintain a constant specific resistance.
Moreover, in the manufacture of electronic material such as semiconductor devices and liquid crystal panels, because various matter that needs to be removed (i.e., particles, organic contaminants, metal contaminants, and the like) is generated during the processes, it is necessary for these to be removed by washing.
One method of washing organic contaminants and metal contaminants that have adhered to electronic material such as a semiconductor substrate or a liquid crystal glass substrate is to employ what is known as RCA washing in which they are washed using washing water obtained by mixing hydrogen peroxide solution and a chemical solution having oxidizability.
However, in this washing method, huge expenses are incurred in the chemical solution, ultrapure water, and waste solution processing, and there is also the problem that there is a heavy burden on the environment.
In recent years, it has been discovered that water that has been obtained by adding small amounts of chemicals and gas components to ultrapure water has the effect of removing impurities from a wafer surface, and that this water demonstrates the same washing effects as conventional highly concentrated chemical solutions.
One technology that uses washing water obtained by adding the aforementioned chemicals and gas components to water is an apparatus for preparing electronic material washing water that has a chemical solution supply apparatus that adds a chemical solution containing acid or alkaline to ultrapure water, and then controls the quantity of chemical solution that is supplied based on the electric conductivity of this chemical solution-containing ultrapure water (see Japanese Patent Application, First Publication (JP-A) No. 2000-208471).
In this conventional method, precise concentration control is possible, however, during actual use there is a possibility that hunting will occur in the concentration if variations occur in the flow rate of the ultrapure water. In addition, the apparatus is complex and the costs involved are high.
Furthermore, if the above chemical solution supply apparatus is used in applications that have an extreme aversion to metal ions (such as, for example, the manufacturing of semiconductors), then it is necessary for the material of components of the chemical solution supply apparatus that come into contact with the solution to be formed from synthetic resin.
Because it is difficult to manufacture miniature flow quantity meters and miniature flow quantity adjusting valves using synthetic resin for solution-contacting components, it is not possible to add highly concentrated original chemical solutions unmodified to ultrapure water. Because of this, it is necessary to use low concentration chemical solutions in which the original solution has been diluted. However, if a low concentration chemical solution is used, then it is necessary to perform a process to adjust the concentration of the chemical agent. This makes it easy for variations to occur in the concentration of the chemical solution.
The present invention was conceived in view of the above described circumstances, and it is an object thereof to provide a supply method and apparatus that make it possible to precisely control supply quantities of a solution being supplied when preparing a solution that can be used as washing water by supplying minute quantities of chemical solution or the like to ultrapure water or the like.